Metal boxes are used to protect hooters from being tampered with. These boxes have openings for propagating the sound produced by the hooters.
In burglar or fire alarm systems, the hooters are usually outside the detection zone and the metal boxes protecting them are fixed with them onto the outside walls or roofs of the protected buildings. These boxes are usually equipped with microinterrupters which cause the hooter to be energized when an attempt is made to tear off the box.
Sabotage is often attempted by sealing off the openings, thus considerably or totally attenuating sound produced by the hooters. Present boxes are not resistant to this type of tampering.